Structural Diversification of <i>Actinidia</i> Trichomes and Modulation by Polyploidization

Fruit trichomes and pericarp architecture are pivotal for biological defense and postharvest resilience in the genus <i>Actinidia</i>. However, the evolutionary diversity of these structures and the molecular mechanisms governing their development—particularly under the influence of polyploidization—remain poorly understood. We performed a systematic evaluation of 21 <i>Actinidia</i> species and 14 cultivars using scanning electron microscopy (SEM) and histological analysis. To determine the effects of genome doubling, an autotetraploid line was induced from diploid <i>A. chinensis</i> cv. ‘Donghong’, followed by comparative transcriptomic and temporal expression profiling. Morphological characterization identified three distinct evolutionary groups based on fruit surface traits: glabrous, caducous-spotted, and persistent-pubescent. All observed trichomes featured a unique bipartite multicellular architecture. Kiwifruit pericarp thickness (59.8–534.6 μm) was locally reinforced at trichome insertion sites. Among kiwifruit cultivars, polyploidization significantly increased both trichome length and total amount. Transcriptomic analysis revealed 235 differentially expressed genes (DEGs) enriched in hormonal signaling and flavonoid pathways. Two key candidate genes, <i>Achv4p15g023764.t1</i> and <i>Achv4p01g000003.t1</i>, were identified as candidate genes for stage-specific regulators governing early morphogenesis and late maturation. By characterizing the morphological diversity and genetic underpinnings of <i>Actinidia</i> trichome and epidermal variation, this study establishes a potential scientific framework for the targeted kiwifruit breeding of novel kiwifruit cultivars with optimized fruit surface characteristics.